This is true. I know the change wasn't just DEI, but I thought it might have been the biggest push. And yeah, after it's gone we will see how much it helped (or not), or other influences will muddy the data and we'll never really know (unless it's a really big trend). shrug
Honestly I think a lot more of it has to do with the perceived status of engineers in society - particularly teenage girls are hyper aware of social status.
15 years ago in any movie a software engineer was considered the biggest loser ever, ridiculed, and unattractive. I think if I had to choose any single thing that increased female participation in engineering the most, it was the Iron Man movies, which showed a vision of high social status in an engineer and started to break the stereotypes.